The present invention relates to a distance measuring device for a camera to measure the distance between the device and an object.
Among the conventional auto focus mechanisms of cameras, an auto focusing system utilizing an infrared LED (Light Emitting Diode) is well known. In this system, a small diameter infrared light beam is radiated to an object to be photographed and the reflected light is received by a semiconductor light position sensing device (PSD) and the like. The distance from the detection output of PSD to the object is computed. According to the computed result, a photographic lens is moved to a predetermined position and the object is photographed.
Conventionally, in such an apparatus, for example, when taking a picture of two persons standing apart from each other a light beam for measuring the distance may not be radiated to them, but may pass between them. Thus, the distance to the background rather than to the persons is measured, and the image of the persons is blurred.
To prevent such an erroneous detection, for example, in Japanese patent provisional publication No. SHO 59-193406, a method for horizontally (linearly) separating an infrared light beam into three beams is disclosed. In this method, the distance measurement range is increased and the beams are radiated to the two persons. Thus, the possibility for erroneously measuring the distance to the background can be reduced.
However, in the method described in the above patent publication, there is no problem when taking a picture while the camera is horizontally positioned. However, when taking a picture while the camera is vertically positioned, the problem as described above still occurs.